1. Field of the Invention
The present invention relates to an electric appliance, and particularly to an electric appliance provided with a time setting means having a simple structure for setting operation time.
2. Description of the Prior Art
An electric appliance such as a microwave oven, electric clothes washer, electric clothes drier, or dishwasher is provided with a time setting device for setting the duration of its operation. FIGS. 1 and 2 show one well-known example of such a time setting device as is used in a microwave oven exemplifying such an electric appliance. This microwave oven employs a microcomputer to control a timer, and its operation time, i.e. the duration of its operation as set by the timer, is entered by the use of a rotary encoder, for example. This type of microwave oven has an operation panel 2 as shown in FIG. 1. The operation panel 2 has, in its upper portion, a display 4 and, in its lower portion, a knob 6 that is operated to rotate a rotary encoder 5 (FIG. 2). In addition, between the display 4 and the knob 6 are provided a start switch 8 and a cancel switch 10. The display 4 is composed of a liquid crystal display device or a fluorescent display device, and serves to display a figure (a value) indicating the operation time (timer-set duration) that is entered by rotating the knob 6 in the direction indicated by an arrow 12.
This microwave oven, which has the operation panel 2 as shown in FIG. 1, is controlled by a control system as shown in FIG. 2. The microwave oven has a magnetron 14 for heating food, a lamp 16 for illuminating the heating chamber, and a fan 18 for cooling the magnetron 14, and these components are controlled by a door switch 20 and a relay switch 22. The relay switch 22 is opened and closed by a controller 24, which receives signals from the start switch 8, the cancel switch 10, and the rotary encoder 5. In relation to the controller 24, a timer 26 is provided.
In this microwave oven, when the knob 6 of the rotary encoder 5 is operated, the operation time, i.e. the duration for which the food is heated, is set according to the angle through which the knob is rotated, and then the operation time thus set is displayed on the display 4. After the operation time is set in this way, a press of the start switch 8 causes the controller 24 to close the relay switch 22. At this time, if the door of the heating chamber is closed, i.e. if the door switch 20 is closed, the magnetron 14 starts oscillating and thereby heating the food in the heating chamber. Simultaneously, the lamp 16 is turned on, and the cooling fan 18 is turned on to cool the magnetron 14. At the same time that the magnetron 14 starts heating, the timer 26 is activated. The timer 26 counts down from the previously set operation time, and the time recognized by the timer 26 as remaining, i.e. the duration for which the heating is still to be continued, is displayed on the display 4. When the timer 26 completes counting the previously set operation time and recognizes that there is no (zero) remaining time, the controller 24 opens the relay switch 22, and turns off the magnetron 14, the lamp 16, and the cooling fan 18.
A press of the cancel switch 10 allows the heating to be stopped at any time. When the cancel switch 10 is pressed, the controller 4 produces a cancellation signal, by the use of which it opens the relay switch 22 and thereby stops the heating that was started as described above. The cancellation signal is fed also to the display 4 to reset to zero the figure displayed thereon.
Such control of an microwave oven provided with a time setting device is disclosed, for example, in Japanese Laid-Open Patent Applications Nos. H 7-190377, H 7-332684, and H 6-241466.
FIGS. 3 and 4 show another well-known example of a time setting device 30, employing light-emitting devices (LEDs), as is used in an electric washer exemplifying another electric appliance provided with a time setting device (according to Japanese Laid-Open Utility Model No. H 1-64836). The time setting device 30 of this washer is provided with a rotary switch having a knob 32 that is rotated to operate the rotary switch, and a time indication panel 35 placed around the knob 32. The time indication panel 35 has markings of figures to indicate the operation time that is currently set. The rotary switch produces a signal containing as many pulses as corresponds to the angle through which the knob 32 is rotated. The washer further has a controller (not shown) for controlling the washer proper, and a timer (not shown) for counting time. The timer counts down from the operation time that is set by the time setting device. The controller controls a series of indicators according to the angle through which the knob 32 is rotated and according to the time recognized by the timer as remaining.
As shown in FIGS. 4A and 4B, in this washer, as the knob 32 is rotated, the controller turns on one of a series of indicators 34 after another so that as many of them as corresponds to the angle through which the knob 32 is rotated are lit simultaneously. Thus, out of the figures marked in the time indication panel 35, that one which is marked at the indicator which is lit last indicates the time that is eventually set.
On the other hand, in another example of a microwave oven shown in FIG. 5, the microwave oven 41 has a door 42 for opening and closing a heating chamber 43 and, on the right thereof, an operation panel 45 for making settings and others. On the operation panel 45 are arranged a time setting knob 49 for setting the cooking time, a power setting knob 53 for setting the heating power, an open/close button for opening and closing the door 41, and others.
The time setting knob 49 has a structure as disclosed, for example, in Japanese Laid-Open Patent Application H 7-119985 and as illustrated in a sectional view shown in FIG. 6. The time setting knob 49 has a boss 49a having a boss hole 49b. A time setting device 47, such as a rotary encoder, is fixed to a control circuit board 46, and its rotary shaft 47a is pressed into the boss hole 49b through a through hole 45a formed in the operation panel 45. The time setting device 47 is fixed, with screws 60, to bosses 59 formed on the back surface of the operation panel 45, with a watertight plate 58 between them.
On the front surface of the operation panel 45, a rib 48 (hereafter also referred to as the "watertight rib") is provided that protrudes so as to encircle the through hole 45a. During cleaning of the operation panel 45 by the use of wet wiping cloth or the like, this watertight rib 48 serves to stop the water that penetrates through the gap a1 between the time setting knob 49 and the operation panel 45 and make it flow around the rib 48 and drop through the gap a2 between the time setting knob 49 and the operation panel 45. In case water drops penetrate inside the operation panel 45, they are discharged by being guided along the watertight plate 58 and then from a ramp 58a formed in it toward the back surface of the operation panel 45.
In the microwave oven described previously, when the knob 6 is rotated, the heating time is set according to the angle through which the knob 6 is rotated, and the thus set heating time is displayed on the display 4. Thereafter, a press of the start switch 8 causes the controller 24 to turn on the relay switch 22 and thereby start heating. The heating is achieved by heating the food put in the heating chamber by the action of microwaves generated through the oscillation of the magnetron 14. Meanwhile, the lamp 16 is lit to illuminate the food being heated so that its condition is visible through the sightglass provided in the door, and a fan motor 18 is rotated to cool the magnetron 14 and a high-voltage transformer 227. In addition, at the same time that the heating is started, the timer 26 is activated so that it thereafter continues counting down from the previously set heating time and displaying the remaining time on the display 4. When the remaining time becomes zero, the relay switch 22 is turned off to stop the heating. Otherwise, the heating can be stopped also by opening the door during heating, in which case the door switch 20 is turned off and the heating is only suspended for a while, or by pressing the cancel switch 10 during heating, in which case the controller 24 turns off the relay switch 22 and thereby stops the heating completely, simultaneously resetting to zero the remaining time of the timer 35 as well as the figure displayed on the display 4.
The well-known electric appliances described above, however, have various disadvantages. For example, in the microwave oven shown in FIGS. 1 and 2, it is practically impossible to change, i.e. increase or decrease, the operation time during heating once it is set by the operation of the rotary encoder 5. That is, to change the operation time, it is necessary to first press the cancel switch 10 to cancel the already set operation time and then operate the rotary encoder 5 again to set a new operation time. Thus, the operation for changing the operation time is rather complicated, and requires an extra component, i.e. the cancel switch 10, for canceling the previously set operation time. This complicates the structure and control of the microwave oven. Moreover, since the knob 6 of the rotary switch and the display 4 for displaying the currently set operation time are placed apart from each other, the operator is obliged to operate the knob 6 while watching the display 4, and therefore this knob 6 is far from user-friendly. Furthermore, since a liquid crystal display device, fluorescent display device, or the like is employed as the display 4, it is inevitable that the microwave oven as a whole is rather expensive.
In addition, the time setting device as used in the microwave oven shown in FIG. 1 employs as its display 4 a liquid crystal display device or fluorescent display device and thus demands high production cost. Such a time setting device is too expensive to be used, for example, in a budget-priced microwave oven that is designed to offer only basic functions and therefore in which the display is expected simply to display the heating time.
On the other hand, in the washer shown in FIG. 3, it is necessary to arrange a series of indicators 34 around the knob 32, and provide a time indication panel 35 further out. This not only leads to a dull layout of the operation panel, for example, in a budget-priced microwave oven that has an operation panel provided only with a heating time setting device, a start switch, and a cancel switch, but also causes the operation panel to occupy an unduly large area and thereby makes the appearance of the microwave oven unappealing.
In the washer shown in FIGS. 3 and 4, it is practically impossible to change, i.e. increase or decrease, the operation time during operation once it is set by the operation of the rotary switch. In addition, in the time setting device 30, the time indication panel 35 is provided separately from the series of indicators 34, and therefore, in dark surroundings, even through it is possible to recognize which of the indicator 34 are lit, it is not easy to recognize the remaining time of the timer.
In the microwave oven shown in FIGS. 5 and 6, in case water drops penetrate inside the watertight rib 48, they flow down along the inner surface of the watertight rib 48 and collect in the lower portion of the watertight rib 48. This promotes the growth of mold. Moreover, although the time setting device 47 can be fixed in position simply by fixing the control circuit board 46 directly to the bosses 59, it is necessary to additionally provide the watertight plate 58 simply to protect electronic components such as the control circuit board from water penetrating inside the operation panel 45. This demands extra cost. Furthermore, although the rotary shaft 47a of the time setting device 47 is pressed into the boss hole 49b of the time setting knob 49, it is still possible to pull out the time setting knob 49 by pulling it with a sufficiently strong force. In such a case, a foreign object may enter through the through hole 45a and, by coming into contact with the control circuit board or other component, cause a malfunction of the microwave oven.
In cases where the heating power needs to be adjusted in steps, it is necessary to use a click mechanism. However, a cooking condition setting device having such a click mechanism is expensive, and therefore using it in place of the time setting device 47 shown in FIG. 6 has been demanding high extra cost.